Luminescence lifetime components in quartz: influence of irradiation and annealing

Pulsed optically stimulated luminescence measured from quartz under certain combinations of annealing and measurement temperature can be resolved into multiple lifetime components. We have studied the influence on these lifetime components of annealing temperature up to 900 °C, beta irradiation dose as high as 1700 Gy, and temperature of stimulation up to 200 °C. Although the time-resolved spectra from which the lifetimes are determined may be measured without heating between irradiation and measurement, a necessary protocol in steady-state optical stimulation applications, studies reported in this paper have been augmented with investigations on the effect of temperature and duration of preheating on the principal and secondary lifetimes. Luminescence spectra for measurements up to 200 Gy consist of a single lifetime but two components occur thereafter, both are independent of radiation dose. The principal lifetime of 35 μs is not affected by temperature of anneal whereas the secondary lifetime increases from 9 to 18 μs when the annealing temperature is changed from 600 to 900 °C. The dependence of both the principal and secondary luminescence lifetimes on measurement temperature can be explained by thermal quenching of the associated luminescence. However, the influence of irradiation, preheating, and annealing on the lifetimes can be explained with reference to an energy band scheme in which the primary mechanism in the processes leading up to luminescence emission is the change in concentration of holes at various luminescence centres caused by annealing

Evaluation of kinetic parameters of traps in thermoluminescence phosphors

A method for evaluating trap depth E, order of kinetics b and frequency factor s from a thermoluminescence (TL) glow peak has been developed. The method is based on using intensities and temperatures at any three points on the glow peak. Unlike similar techniques that provide no expression for frequency factor, the present formulation provides such an expression. The expression does not require knowledge of the temperature at which maximum intensity occurs, a parameter not usually known accurately from experimental glow peak data. For the method, it is found that use of points in the ascending part of the glow peak where the intensities are less than 10% maximum intensity gives parameter values closest to the true ones. Possible reasons for getting less accurate results when points are taken beyond this region are discussed. Values of the activation energy calculated using the present technique were always close to the true value. However, the frequency factor only approaches the true value as the dose given to the sample approaches saturation. When the three data points are selected in the initial-rise region, the equation for evaluating E in the method described in this paper becomes a two-point version of the initial-rise method. The advantage of the present technique over the initial-rise method is that it also gives b and hence s. The method is used to analyse the TL glow curve of a gamma-irradiated sample from Ijero-Ekiti, Nigeria

Anomalous behaviour of thermoluminescence from quartz: a case of glow peaks from a Nigerian quartz

Anomalous behaviour displayed by a thermoluminescence (TL) glow peak as radiation dose increases in a Nigerian quartz is presented. The glow curves of the phosphor have four clear glow peaks. The peak temperatures of the first three glow peaks were found to be constant with change in radiation dose at 82, 148 and 200ºC for the sample readout at a heating rate of 1ºCs[superscript (-1)]. The peak temperature of the fourth peak, which is at around 320ºC for a sample irradiated to a dose of 63 Gy and heated at 1ºCs[superscript (-1)], displays anomalous behaviour with increase in dose relative to the first three peaks. The temperature at which this peak occurs increases with dose to about 335ºC for 177 Gy and then decreases thereafter as dose is further increased. The change is explained on the assumption that the peak may be complex consisting of several overlapping first-order glow peaks each with different TL behaviour

Time-resolved luminescence of low sensitivity quartz from crystalline rocks

preprintTime-resolved luminescence spectra of low sensitivity natural quartz from crystalline rocks are presented. The luminescence was pulse-stimulated at width using 470 nm blue light from quartz separated from plutonic, metamorphic, volcanic and hydrothermal samples. Measurements were made at 20 °C. All samples show evidence of a short lifetime component less than long although in several cases too weak in intensity to be evaluated accurately. On the other hand, the value of the principal lifetime component varies considerably being about in metamorphic quartz, in plutonic quartz, and in one example of hydrothermal quartz. The results illustrate a new feature of luminescence from quartz for which lifetimes less than or greater than have never been reported at room temperature before. It is argued that the thermal provenance of the quartz and so the annealing it will have experienced influences the size of the observed lifetime. In particular, the results are explained in terms of a model consisting of three luminescence centers with the dominant lifetime linked to preferential recombination at one center depending on the thermal history of the sample and hence the hole concentration of the center

Relative features of the principal and secondary luminescence lifetimes in quartz

Quartz is a common natural mineral with properties that make it amenable for application in radiation dosimetry using luminescence methods [1]. The luminescence properties of quartz including its sensitivity and luminescence lifetimes undergo notable changes when the quartz is annealed, and in particular, near its phase inversion temperatures of 573 and 867 oC [2, 3]. The physical processes leading up to the emission of luminescence in quartz may be investigated using time-resolved optical stimulation. The aim of this method is to separate in time the stimulation and emission of luminescence to enable measurement of time-resolved luminescence spectra which may be resolved into associated lifetimes, defined in this sense as the delay between stimulation and emission of luminescence [4, 5]. A number of such studies show that annealing defines the detailed distribution of lifetimes with measurement temperature as well as the irradiation-dependent characteristics of the lifetimes [3, 6]. In particular, it was noted [3] that spectra measured at certain temperatures could be accurately resolved into more than one component, a scenario that pointed to the possibility of involvement of multiple luminescence centers in the emission of luminescence from quartz. The aim of this work is to build on the findings described, specifically to study the influence of measurement temperature and irradiation on the principal and subsidiary luminescence lifetimes in natural quartz

Comparative antibacterial studies of mistletoes growing on two diffrent host plants in Akure North, Nigeria

The antibacterial activity of 60 % methanolic leaves extracts of mistletoes (Viscum album) growing on cocoa and cola trees were tested on Bacillus cereus, Pseudomonas aeruginosa,Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Salmonella typhi in vitro. Both the gram-positive and gramnegative organisms showed variable sensitivity to the extracts treatments. The results obtained indicated that extracts from both host plants had some antibacteria activities against the microorganisms when compared with standard antimicrobial agents (ciprofloxacin and sterptomycin) used as positive controls at P < 0.05 significant level. In general,extracts from cocoa (Theobroma cacao) plant showed more antimicrobial tendency than those from cola (Kola nitida) plant

Physico-Chemical Properties of Yellow Oleander (Thevetia peruviana) and their effects on the Qualities of Biodiesel

This study investigated the effects of physico-chemical properties of Yellow oleander (Thevetia peruviana) on quality of biodiesel. The seeds were processed and extraction of oil was carried out using solvent extraction method. Biodiesel was produced from the extracted oil using trans esterification process. Physical and chemical properties of Thevetia peruviana biodiesel were determined using the ASTM standard test procedures. Results showed that the biodiesel contained little sulphur (3.0 mg/kg) and exhibited a high cetane number of 55 that exceeded the standard limit of 47 and 51 prescribed for EN 14214 and EN 590 respectively, which is a good indication of fuel’s ignition and combustion quality. Kinematic viscosity of the biodiesel at 40°C was 4.81 mm2/s, which was within the range specified by EN 14214. The density at 15°C was found to be 0.89g/cm3&nbsp;which was well within the range specified by EN 14214. 0.16 mg/g of acid level was obtained for the bio-diesel, which conformed to the standard set by &nbsp;Calorific value of the biodiesel produced from Yellow oleander seed oil was obtained as&nbsp;40.42 kJ/g which indicated good fuel properties such as density, ignition quality, viscosity, cetane number, heating value and flash point. Carbon residue of the biodiesel was 0.14 mass %. Quality of the biodiesel produced conform to biodiesel and petroleum diesel standards of EN14214 and EN590 respectively

Paediatric brought-in-dead at a tertiary health facility in South western Nigeria: Patterns and drivers

Background: ‘Brought- in-dead’ (BID) refers to the demise of an individual before presentation to a health facility. This study assessed the pattern of paediatric BID cases seen at a tertiary health facility in southwest Nigeria. Method: A cross-sectional, descriptive study was done at the Children Emergency Ward (CEW) of the hospital between January 2014 and December 2018. The patterns of BID cases and presumed causes of death were determined using a standardized checklist adapted from the WHO verbal autopsy instrument. Results: Ninety-eight BID cases were seen during the study, constituting 2.5% of total patients seen during the period. The median (IQR) age of cases was 24.0 (8.75 – 63.0) months and 72.4% were under-fives. Most had symptoms related to the haematologic (36.7%), respiratory (24.5%) or digestive (20.4%) systems. Severe anaemia 31(31.6%), gastroenteritis 19 (19.4) and aspiration 17 (17.3%) were the most common causes of death. The median (IQR) duration of illness before presentation was 3.0 (1.0 – 7.0) days but most presented from 4 – 7 days of illness. A significant relationship was found between the duration of illness and whether or not pre-hospital treatment was received (p &lt; 0.0001). Unprescribed drugs purchased over the counter were the most commonly used treatment in 79.1% of cases (p &lt; 0.0001). Conclusion: This study has highlighted the prevalence and pattern of paediatric BID in a tertiary health facility in southwest Nigeria and the factors that were associated with it. More efforts need to be geared towards community sensitization and pediatric health care to prevent factors drivingits menace

Reduced Plasma Levels of 25-Hydroxycholesterol and Increased Cerebrospinal Fluid Levels of Bile Acid Precursors in Multiple Sclerosis Patients

Multiple sclerosis (MS) is an autoimmune, inflammatory disease of the central nervous system (CNS). We have measured the levels of over 20 non-esterified sterols in plasma and cerebrospinal fluid (CSF) from patients suffering from MS, inflammatory CNS disease, neurodegenerative disease and control patients. Analysis was performed following enzyme-assisted derivatisation by liquid chromatography-mass spectrometry (LC-MS) exploiting multistage fragmentation (MS n ). We found increased concentrations of bile acid precursors in CSF from each of the disease states and that patients with inflammatory CNS disease classified as suspected autoimmune disease or of unknown aetiology also showed elevated concentrations of 25-hydroxycholestertol (25-HC, P &#60; 0.05) in CSF. Cholesterol concentrations in CSF were not changed except for patients diagnosed with amyotrophic lateral sclerosis (P &#60; 0.01) or pathogen-based infections of the CNS (P &#60; 0.05) where they were elevated. In plasma, we found that 25-HC (P &#60; 0.01), (25R)26-hydroxycholesterol ((25R)26-HC, P &#60; 0.05) and 7α-hydroxy-3-oxocholest-4-enoic acid (7αH,3O-CA, P &#60; 0.05) were reduced in relapsing-remitting MS (RRMS) patients compared to controls. The pattern of reduced plasma levels of 25-HC, (25R)26-HC and 7αH,3O-CA was unique to RRMS. In summary, in plasma, we find that the concentration of 25-HC in RRMS patients is significantly lower than in controls. This is consistent with the hypothesis that a lower propensity of macrophages to synthesise 25-HC will result in reduced negative feedback by 25-HC on IL-1 family cytokine production and exacerbated MS. In CSF, we find that the dominating metabolites reflect the acidic pathway of bile acid biosynthesis and the elevated levels of these in CNS disease is likely to reflect cholesterol release as a result of demyelination or neuronal death. 25-HC is elevated in patients with inflammatory CNS disease probably as a consequence of up-regulation of the type 1 interferon-stimulated gene cholesterol 25-hydroxylase in macrophage